Mycoplasmal pneumonia of swine caused by the bacterial pathogen Mycoplasma hyopneumoniae is a widespread chronic respiratory disease in pigs. Especially young piglets are vulnerable to this, non-fatal, disease. The enzootic pneumonia is a chronic disease that results in poor feed conversion and stunted growth. The disease is highly contagious and transmission is usually through direct contact with infected respiratory tract secretions, e.g. in the form of infected droplets after coughing/sneezing.
The most problematic consequence of this disease is that it predisposes for all kinds of secondary infections of the respiratory system.
It is estimated that e.g. in the USA, 99% of all pig farms are infected. Yearly losses are estimated to be between 100 and 300 million dollars.
Another very frequently encountered respiratory disease in pigs is the disease commonly known as Porcine Reproductive Respiratory Syndrome (PRRS), and as Porcine Epidemic Abortion and Respiratory Syndrome (PEARS). Currently the disease is world-wide referred to as PRRS. The pathology is not restricted to respiratory disease but also to abortion. Other symptoms, usually or occasionally seen with the disease are: off feed, anorexia, bluish discolorations of the extremities, especially the ears.
The causative agent of the disease is now known to be a small enveloped RNA virus. In breeding females, PRRS causes fever, depression, and decreased appetite in sows and gilts. Reproductive problems will follow and affect primarily females in late gestation.
In young pigs, PRRS predominately affects the respiratory system. Abnormally rapid breathing or “thumping” is observed. The severity of problems from other bacterial and viral pathogens often will seem to intensify, with death losses and treatment costs ensuing. Poor performance may follow, with pigs taking extra weeks to finish.
In addition to the frequently seen diseases caused by Mycoplasma hyopneumoniae and PRRS virus, currently an economically significant respiratory disorder in pigs is more and more frequently seen. This disorder is characterized by slow growth, decreased feed efficiency, lethargy, anorexia, fever, cough and dyspnea. It is commonly known now as porcine respiratory disease complex (PRDC), and the two most common pathogens isolated from pigs suffering from PRDC are Mycoplasma hyopneumoniae and PRRS virus. Apparently, the disease is caused by some combined action of the two pathogens.
The pig farming industry benefits from the presently available efficacious vaccines against Mycoplasma hyopneumoniae infection and PRRS virus infection. And since especially young piglets are vulnerable to Mycoplasma hyopneumoniae infection as well as PRRS virus infection, it would seem most efficient to vaccinate against both diseases at the same early moment in time.
It has however become evident over the years that this is not an option. It is now an established fact that the efficacy of Mycoplasma hyopneumoniae vaccines significantly decreases if pigs become either infected or vaccinated with PRRS virus. This effect is seen if infection or vaccination with PRRS virus takes place during vaccination or even 1-2 weeks after vaccination with a Mycoplasma hyopneumoniae vaccine. Even avirulent vaccine strains of PRRS virus show this effect (Pig International 30: 9-12 (2000), Thacker, E. L. et al., J. Clin. Microbiol. 37: 620-627 (1999), Thacker, E. L. et al, Vaccine 18: 1244-1252 (2000)).
In addition, it was shown that PRRS-infection induces a very rapid onset of the pathology of a Mycoplasma hyopneumoniae infection.
Moreover, Mycoplasma hyopneumoniae infection increases the duration and severity of viral infections in general, such as PRRS (Thacker, E. L. et al., Vaccine 18: 1244-1252 (2000)) and Swine Influenza (Thacker, E. L. et al., J. Cl. Microbiol. 39: 2525-2530 (2001)). This is an additional reason to vaccinate against viral infections such as PRRS and Swine Influenza as soon as possible after birth, but anyway before Mycoplasma hyopneumoniae strikes.
Thus, for the reasons mentioned above, there is a strong preference to first vaccinate with PRRS-virus vaccine, instead of applying both a PRRS-virus vaccination and a Mycoplasma hyopneumonia vaccination. As a consequence however, one has to wait until the live attenuated PRRS vaccine strain has disappeared from the body. This means that one has to wait for at least two to three weeks and preferably longer, before a first (priming) Mycoplasma hyopneumonia vaccine can safely be administered and even four weeks and preferably longer, before giving the second vaccination (booster vaccination) with Mycoplasma hyopneumonia vaccine. As another consequence, the piglets will remain unprotected against Mycoplasma hyopneumonia infection for at least four weeks after PRRS-vaccination.
However there are currently no ways to circumvent these undesired consequences.